The present invention relates to multilayer pressure-sensitive adhesive (PSA) constructions that exhibit a balance of high adhesive performance (including low temperature performance), good convertibility, improved wet-out on plastic substrates, improved haze and low contaminant build-up in printers for paper and film applications.
PSAs and self-adhesive labels are now used extensively in the home, in offices and in many commercial settings. In a typical construction, a removable release liner is coated with a PSA, which is laminated to a label facestockxe2x80x94typically an imprintable paper or plastic film. Removal of the release liner allows the label to be adhered to a substrate. Alternatively, the PSA can be directly coated onto the facestock. Such constructions are typically produced in large (e.g., 79xe2x80x3 wide) rolls, which are then slit into smaller (e.g., 11xe2x80x3 wide) rolls. Label sheets are made by cutting the resulting rolls into sheets, for example, 8xc2xdxe2x80x3xc3x9711 sheet, A4 sheets or 5xe2x80x3xc3x978xe2x80x3 sheets. Individual labels are fabricated by die-cutting the construction before the sheeting step, and, optionally, the label sheet is matrix-stripped. In contrast, tapes usually do not require die-cutting and sheeting. Labels are also typically capable of being machine-printed, while tapes are typically not printed.
The adhesives used in PSA labels and tapes include rubber-based polymers (usually tackified with one or more tackifiers that improve overall adhesion to various substrates), and acrylic polymers (which may be inherently tacky or are compounded with a tackifier). PSAs can be applied to a release liner or facestock from an organic solvent, from an aqueous dispersion, or as a hot melt.
A good PSA label should exhibit a number of desirable properties, including, for example, sufficient shear, peel adhesion, tack, and quickstick, to a variety of substrates, and at various temperatures. In other words, the labels should exhibit sufficiently high adhesion to the substrate(s) on which they are to be used over a range of temperatures. However, PSAs that exhibit sufficiently high adhesion, particularly at low temperatures, generally tend to exhibit high flow. As a result, such PSAs tend to exhibit relatively low convertibility; they tend to ooze from the edges of the construction during converting. The ideal PSA label would not only perform well on a variety of substrates at various temperatures, but would also convert well.
The cost of converting an adhesive laminate into a finished product is a function of the speed and efficiency at which it undergoes converting operations, including die-cutting and matrix-stripping to leave labels on a release liner, butt-cutting of labels to the release liner, marginal hole punching, perforating, fan folding, guillotining and the like, and optionally printing. Die-cutting involves cutting of the laminate to the surface of the release liner. Hole punching, perforating and guillotining involve cutting cleanly through the label laminate. While the nature of all layers of the laminate can impact the ease and cost of convertibility, the adhesive layer typically has been the greatest limiting factor in each type of converting operation. This is due to the viscoelastic nature of the adhesive, which hampers precise and clean penetration of a die in die-cutting operations and promotes adherence to die-cutting blades and the like in cutting operations. Stringiness of the adhesive may also impact matrix-stripping operations, which typically follow die-cutting operations. Thus, it is desirable to balance adhesive performance with convertibility.
Printing is an optional step during label converting. In the case of unprinted labels, such as office and personal computer labels, printing occurs during use of the labels. A desirable property of office and computer labels for laser printers is high laser printer performance, i.e., reduced contaminant build-up in a laser printer when a large number of label sheets are run through the printer. Unfortunately, many PSA label sheets, when passed through the laser printer, leave a residue containing PSA on the photoreceptor roll, fuser bar, roller and/or other parts of the printer. Printer performance, like convertibility, is generally a function of the flowability of the adhesive.
Another desirable property of some PSAs is good wet-out on plastic substrates. However, this property, like adhesion, generally increases with adhesive flowability. Thus, as wet-out on plastic substrates is improved, convertibility is sacrificed.
Still another desirable property for some applications is adhesive clarity. Many adhesive labels are designed to be clear, for example, where they will be applied to clear bottles. The adhesive used in such labels, when applied to a rough surface, should be clear, i.e., not hazy, so that the adhesive is not visible through the clear facestock of the label. This property is related to wet-out in the case of clear film or plastic labels for plastic substrates, in that poor wet-out tends to cause loss of clarity during application of such labels.
Thus, a need exists for a PSA label construction that achieves a good balance of the above-described properties, particularly adhesive performance, convertibility, and laser printer performance.
According to the present invention, there are provided multilayer PSA label constructions that achieve a good balance of properties, namely, adhesive performance, convertibility, and laser printer performance, and, optionally, good wet-out on plastic substrates and low haze. In one embodiment, the invention is directed to a multilayer PSA construction comprising a paper or film facestock, a multilayer adhesive coating, and a release liner. The adhesive coating is made of a face side adhesive (FSA) layer comprising a first emulsion acrylic PSA, which is in contact with the inner surface of the facestock, and a liner side adhesive (LSA) layer, comprising a second emulsion acrylic PSA different from the first acrylic PSA, which is in contact with the FSA. The adhesive coating has a coat weight of less than about 26 g/m2 and a flow of less than about 50 microns (xcexcm) at room temperature. The construction exhibits a loop tack value of at least about 3.5 N/25 mm at 5xc2x0 C. on a polyethylene substrate, particularly when the facestock is 50 lb uncoated, wood-free, sized 2-sides label stock. It has been discovered that multilayer PSA label constructions exhibiting these properties also exhibit good convertibility and laser printer performance.
In another embodiment, the invention is directed to a method for minimizing contaminant build-up in a printer caused by extended printing of adhesive labels. The method comprises repeatedly passing through the printer a PSA label sheet comprising a paper or film facestock, a multilayer adhesive coating and a release liner. The adhesive coating is made of an FSA layer comprising a first acrylic PSA in contact with the inner surface of the facestock, and an LSA layer comprising a second acrylic PSA, which is different from the first acrylic PSA, in contact with the FSA.
In yet another embodiment, the invention is directed to a multilayer PSA label construction exhibiting good printer performance and good adhesive performance. The PSA label comprises a facestock, an FSA layer in contact with the facestock, an LSA layer in contact with the FSA layer, and a release liner in contact with the LSA layer. The FSA layer comprises a first acrylic PSA, and the LSA layer comprises a second acrylic PSA different from the first acrylic PSA. The construction, particularly when made with a 50 lb uncoated, wood-free, sized 2-sides label stock, exhibits (i) a loop tack value of at least about 3.5 N/25 mm at 5xc2x0 C. on a polyethylene substrate, and (ii) good printer performance, i.e., reduced contaminant build-up in a laser printer when a large number of label sheets are run through the printer, as demonstrated by a defect area of less than 50 mm2 on a black-out sheet that was passed through a laser printer through which at least about 2500 sheets of the construction have been fed.
In still another embodiment, the invention is directed to a multilayer PSA label construction exhibiting a good balance of adhesive performance, convertibility, and laser printer performance. The multilayer PSA label construction comprises a facestock, an FSA layer in contact with the facestock, an LSA layer in contact with the FSA layer, and a release liner in contact with the LSA layer. The FSA layer comprises a first acrylic PSA, and the LSA layer comprises a second acrylic PSA, different from the first acrylic PSA. The first acrylic PSA exhibits a flow of less than about 40 xcexcm. The second acrylic PSA is selected based on its low temperature adhesive performance. The second acrylic PSA exhibits a loop tack value at 5xc2x0 C. on polyethylene of at least about 3.75 N/25 mm, particularly when part of a construction comprising a 50 lb uncoated, wood-free, sized 2-sides label stock.
In another embodiment, the invention is directed to a multilayer PSA label construction comprising a paper or film facestock, an FSA layer in contact with the facestock, an LSA layer in contact with the FSA layer, and a release liner in contact with the LSA layer. The FSA layer comprises a first acrylic PSA, and the LSA layer comprises a second acrylic PSA different from the first acrylic PSA. The construction, particularly when made with 50 lb uncoated, wood-free, sized 2-sides label stock, exhibits a loop tack value of at least about 3.5 N/25 mm at 5xc2x0 C. on a polyethylene substrate. The FSA and LSA, when taken together, exhibit a haze value of less than about 60%. The label constructions of this embodiment are particularly useful for use as clear labels when used with a clear film facestock. They exhibit a balance of good adhesive performance and good clarity.
Another embodiment of the invention is directed to a multilayer PSA label construction that exhibits good convertibility and good adhesive performance. The multilayer PSA construction comprises a film or paper facestock, an FSA layer in contact with the facestock, an LSA layer in contact with the FSA layer, and a release liner in contact with the LSA layer. The FSA layer comprises a first acrylic PSA, and the LSA layer comprises a second acrylic PSA different from the first acrylic PSA. The FSA layer and LSA layer, when part of the construction, have a combined specified thickness. The multilayer construction, when cut by a slitting knife in a converting operation, exhibits less contaminant build-up on the slitting knife than a comparable adhesive construction comprising a single layer of the LSA applied in an amount such that the single layer has the specified thickness. Preferably, the multilayer construction, particularly when made with 50 lb uncoated, wood-free, sized 2-sides label stock, exhibits a loop tack value of at least about 3.5 N/25 nm at 5xc2x0 C. on a polyethylene substrate.
Another embodiment of the invention is directed to a multilayer PSA label construction that exhibits good convertibility with respect to matrix-stripping. The multilayer PSA construction comprises a film or paper facestock, an FSA layer in contact with the facestock, an LSA layer in contact with the FSA layer, and a release liner in contact with the LSA layer. The multilayer construction, when cut by a matrix-stripping die, exhibits less adhesive build-up on the die than a comparable adhesive construction having a single layer of the LSA PSA applied in an amount such that the single layer has the specified thickness.
The invention is further directed to a method of producing a multilayer PSA adhesive construction, and to a method of producing unprinted label sheets for use with laser printers based upon such multilayer PSA construction. The multilayer PSA construction comprises a paper or film facestock, a multilayer adhesive coating and a release liner. The adhesive coating is made of an FSA layer comprising a first acrylic PSA in contact with the inner surface of the facestock, and an LSA layer comprising a second acrylic PSA, which is different from the first acrylic PSA, in contact with the FSA. The method comprises providing a release liner and a facestock that is suitable for machine-printing. A first emulsion acrylic adhesive layer (the LSA) is applied to an inner surface of the release liner. A second emulsion acrylic adhesive layer (the FSA) is applied to the first acrylic adhesive layer. The facestock is applied to the second emulsion acrylic adhesive layer to form an adhesive construction. The adhesive construction is cut to form unprinted labels on the release liner. Such labels have the property of minimizing contaminant build-up in a printer caused by extended printing of adhesive labels, measured by repeatedly passing through the printer PSA label sheets produced by this method. In a preferred embodiment, the LSA and FSA are applied simultaneously, such as by a multilayer coating die.